http://www.preference-audio.com/phaseplug.htmFirst paragraph:
"In any conventional loudspeaker, the highest frequencies of audio emanate from the area around the center of the cone
and the lower frequencies are produced by the area of the cone that is farther from the center. In fact, the distance
from the center at which a sound wave will come off a loudspeaker cone is directly related to its frequency.
This helps explain why larger cone loudspeakers are usually capable of producing more bass."

There is something to be said for localization of high frequencies in the center of a driver, but I think that's were that article leaves the fact highway.

Drivers all the way down to less than an inch can reproduce the bottom octave of "audio". At a low level of course, but I think that is a good indicator of the relationship between diameter and frequency.

"Once again, it is NEVER the gear that makes a good record.It just fills Forum pages..." --compasspnt

This makes more sense to me:
"Second, all frequencies are radiated from all moving parts of the cone. When you place a mic at the center of the cone, it is closest to equidistant from each point on the cone. The distances that sound must travel from each point on the cone to the mic are very similar, and therefore the contributions from each part of the cone sum coherently. When you place the mic in an off-center position, the distances that sound must travel from parts of the cone to the mic vary over a much wider range. This causes phase and amplitude differences between arrivals from different parts of the cone. The phase differences cause cancellations, and, due to their shorter wavelengths, the cancellations are greater at higher frequencies. "- Jay Mitchell.
http://www.thegearpage.net/board/showth ... 956&page=3

Also, I don't question that the phase plug effects how sound radiates from a speakers.
I am speculating that it works in a similar fashion to this:
http://www.webervst.com/blocker.htmlIt's pretty much just a dust cap mounted on a stick.